Chamfer device for cutting packaging materials

ABSTRACT

A chamfer cutting device for cuffing packaging materials comprises a die and a knife part which has a plurality of knives. The die can be moved toward the knife part in order to carry out a cut. The knives are arranged individually in the knife part in a force-dependent manner in such a way that their position with respect to the tool plate varies in a defined way as a function of the force produced by contact with the packaging material or the die. In the event of contact between the knife and the die, a force acts on the knife which does not exceed a predefined maximum force. The chamfer cutting device has the advantage that the die can be guided right up to the knives.

The present invention relates to a chamfer cutting device for cuttingpackaging materials.

Packages, such as yogurt pots, are often produced nowadays by beingshaped and separated from a stream of thin sheet. The thin sheets usedin this case are generally plastic films or metal foils, for examplemade of polystyrene, polyethylene, polypropylene or aluminum, and inparticular composites thereof.

In order to separate packages, chamfer cutting devices may be used,which have a die and a knife part having a large number of knives andpunches. The packaging material stream, in which the individual packagesare normally already shaped, is introduced between the die and the knifepart. The die and the knife part are then moved toward each other, as aresult of which the packaging material is clamped, punched by thepunches and cut by the knives. Finally, the die and knife part are movedapart again, it being ensured that the packaging material separates fromthe knife part and the die in order that the packaging material streamcan be advanced further. The separation of the packaging material isachieved, for example, by means of sprung strippers on the side of theknife part and, on the side of the die, by pulling the latter away.

The packaging material can either be cut through completely by theknives or it can also be only chamfered, that is to say a cut can bestarted, the latter leading to the formation of intended dividingpoints, such as are known, for example, from coherent yogurt pots.Whether a knife cuts completely through the packaging material whencarrying out a cut or only begins to cut it, depends on how close thedie and the knife are guided toward each other, complete severing of thepackaging material occurring depending on the packaging material atdifferent minimum distances between die and knife.

Since it is very difficult to guide the die and the knives exactlytoward each other when carrying out a cut, and since in additiondifferences can occur between the individual knives with respect to theminimum distance between knife and die which, for example, are based ondifferent wear, on production tolerances or on different deformations inthe chamfer cutting device, it is never possible for all the knives andthe die to be guided completely against one another, so that in the caseof most knives, there is no contact with the die. As a rule, with regardto minimizing the wear, a distance between the knives and the die iseven deliberately left, this distance being different from knife toknife as a result of the aforementioned influences. However, this hasthe disadvantage that, in particular, tough packaging materials, such aspolypropylene, are often not cut through cleanly. In addition, anydifferences between the individual knives with respect to the minimumdistance between knife and die can lead to different cut results.

In view of the disadvantages of the previously known chamfer cuttingdevices described above, the invention is based on the following object.To be provided is a chamfer cutting device of the type mentioned at thebeginning which, with the lowest possible wear on the knives, permits aclean execution of a cut with high process reliability, in particulareven in the case of tough packaging materials.

This object is achieved by the chamfer cutting device according to theinvention.

The nub of the invention is that, in a chamfer cutting device forcutting packaging materials, having a die and a knife part which has atleast two knives, it being possible for the die and the knife part to bemoved relative to each other in order to carry out a cut, at least oneof the knives is arranged in the knife part in a force-dependent mannerin such a way that its position with respect to a tool plate varies in adefined way as a function of the force produced by contact with apackaging material or the die, in the event of contact between the knifeand the die a force acting on the knife which does not exceed apredefined maximum force.

The fact that at least one of the knives in the knife part is arrangedin a force-dependent manner means that differences between individualknives with respect to the minimum distance between knife and die can becompensated for when carrying out a cut. Since the knife arranged in aforce-dependent manner can change its position as a function of theforce exerted by the packaging material or by the die on the knife, thatis to say can retreat, for example, and since, even in the case ofcontact between knife and die, a predefined maximum force is notexceeded, unnecessarily high forces on the knife and thereforeunnecessary material stresses and unnecessary wear, in particularmaterial fatigue and deformation of the knife edge, can be avoided orminimized. In addition, it is not necessary to replace a knife that isworn more severely than the others immediately, since the wear-inducedshortening of individual knives is compensated for by lesser retreat ofthese knives.

The chamfer cutting device is advantageously designed and controlled insuch a way that the at least one knife arranged in a force-dependentmanner comes into contact with the die when a cut is being carried outby moving the knife part and the die toward each other. Guiding theknife and the die completely together results in clean severing even oftough packaging materials.

Each of the knives in the knife part coming into contact with the diewhen a cut is being carried out is advantageously arranged in aforce-dependent manner, individually or together with other knives ingroups, such that its position with respect to a tool plate varies in adefined way as a function of the force produced by contact with apackaging material or the die, in the event of contact between the knifeand the die a force acting on the knife which does not exceed apredefined maximum force. The die can then be guided completely up toall these knives or all these knives can be guided completely up to thedie.

The predefined maximum force is advantageously adjustable. Thisadjustment can be used, for example, in order to adapt to a specificpackaging material.

It has been shown that the chamfer cutting device is advantageouslydesigned and controlled in such a way that when a cut is being carriedout by moving the knife part and the die toward each other, a force ofat most 1000 N per mm knife length, preferably 10–100 N per mm knifelength and per mm thickness of the packaging material to be cut, acts onthe knives. Under these forces, the knives do not become wornunnecessarily quickly. In order to carry out a good cut, on the otherhand, a dividing force of at least 10 N per mm knife length and per mmmaterial thickness is generally needed, depending on the packagingmaterial.

The arrangements of the individual knives in the knife part canadvantageously be changed over between a cutting position and achamfering position, in the cutting position, when carrying out a cut, aknife cutting completely through the packaging material arranged betweenthe knife and the die, while in the chamfering position, a knife onlybeginning to cut the packaging material arranged between the knife andthe die. This permits the cutting configuration to be changed in astraightforward manner.

In a preferred design variant, a knife is arranged to receive a variableforce; the knife is mounted on the tool plate via a gas piston, therepreferably being means for feeding gas into and removing gas from a gaschamber of the gas piston, which makes it possible to adjust thedependence of the position of the knife with respect to the tool platebased on a variable force which acts on the knife. This adjustment canbe used, for example, to adapt to a specific packaging material.

In an alternative, advantageous design variant, a liquid medium is usedinstead of a gas.

In yet another preferred design variant, to arrange a knife in aforce-dependent manner, the latter is mounted on a tool plate by meansof at least one resilient part, preferably one or more compressionsprings or a rubber cushion. There is preferably at least one direct orindirect stop for the knife, which limits the compression of theresilient part by the knife, in that, for example in the event of a highlevel of retreat of the knife, it absorbs the forces acting togetherwith the knife. As a result, the resilient part is protected againstinadmissibly high deformations or stresses.

In an advantageous design variant, at least one of the knives in theknife part is arranged to retreat in a force-dependent manner in such away that under a loading which is less than a limiting force, itmaintains its position, and under a loading which is greater than thislimiting force, it retreats. As soon as the die exerts a force on theknife which is higher than the limiting force, the knife retreats. Inthis way, unnecessary wear or damage to the knife can be avoided, forexample in the event of a foreign body present at the cutting locationon the packaging material.

There is advantageously a stop for each knife in the knife part, onwhich the knife is supported directly or indirectly in the chamferingposition when carrying out a cut. The stop is preferably adjustable, sothat the cut depth can be varied. In the case of simple part cutting orchamfering, the die and the knife are not brought into contact, so thatforce-dependent arrangement of the knife does not normally provide anyadvantage.

There is preferably a stop, preferably an adjustable stop, for eachknife in the knife part, on which the knife is supported directly orindirectly when carrying out part of a cut, in which a comparativelygreater cutting force is required, while during the remainder of thecut, in which a comparatively smaller cutting force is required, it isspaced apart from the stop. As soon as the force acting on the knifereaches a specific value, the knife is supported directly or indirectlyon the stop. If the force acting on the knife falls below this specificvalue again, for example at the end of the cutting operation, the knifeis moved into a position closer to the die as a result of theforce-dependent arrangement, or it is moved completely against the dieand the packaging material is severed completely. One advantage of thisstop is that the force that acts to the maximum extent in the event ofcontact between the knife and the die can be predefined smaller than theforce needed to cut the packaging material.

In the following text, the chamfer cutting device according to theinvention will be described in more detail using four exemplaryembodiments and with reference to the appended drawings, in which:

FIG. 1 shows a sectional view of a first exemplary embodiment of thechamfer cutting device according to the invention, having knives,arranged in a force-dependent maimer by means of gas pistons, and stopsfor the chamfering position;

FIG. 2 shows a view from below of the knife part of the chamfer cuttingdevice of FIG. 1;

FIG. 3 shows a detail of the chamfer cutting device of FIG. 1 in thecutting and punching position;

FIG. 4 shows a sectional view of part of the chamfer cutting deviceaccording to the line I—I in FIG. 1, with a packaging material streambefore being cut;

FIG. 5 shows, schematically, the chamfer cutting device according toFIG. 4 during cutting and chamfering or initial cutting of the packagingmaterial;

FIG. 6 shows a sectional view of part of a second exemplary embodimentof the chamfer cutting device according to the invention, having knivesarranged in a force-dependent maimer by means of gas pistons;

FIG. 7 shows the chamfer cutting device according to FIG. 6 in thecutting and punching position;

FIG. 8 shows a sectional view of part of a third exemplary embodiment ofthe chamfer cutting device according to the invention, having knivesarranged in a force-dependent manner by means of compression springs;

FIG. 9 shows the chamfer cutting device according to FIG. 8 in thecutting and punching position;

FIG. 10 shows a sectional view of part of a fourth exemplary embodimentof the chamfer cutting device according to the invention, having knives,arranged in a force-dependent manner by means of compression springs,and stops for supporting the knives;

FIG. 11 shows a chamfer cutting device according to FIG. 10 in a firstcutting and punching position;

FIG. 12 shows the chamfer cutting device according to FIG. 10 in asecond cutting and punching position; and

FIG. 13 shows a sectional view of a fifth exemplary embodiment of thechamfer cutting device according to the invention.

FIRST EXEMPLARY EMBODIMENT—FIGS. 1 TO 5

The first exemplary embodiment illustrated of a chamfer cutting deviceaccording to the invention comprises, as a framework, a table plate 7and a top plate 70, which are connected to each other by a total of fourconnecting columns 71, of which two are visible in FIG. 1. Fixed to thetop plate 70 is a tool plate 4, to which in turn a punch holding plate31 is fitted. Arranged on the tool plate 4 and the punch holding plate31 are a total of four knives 2 which together approximately form asquare, four stops 25, four punches 3, eight strippers 5 and two guidecolumns 41. The elements arranged directly and indirectly on the toolplate 4 will also be referred to together as the knife part within thecontext of the present description.

The two guide columns 41 each project into a guide column channel 14,which is formed in a die base 13 and a die plate 11 fitted thereto. Thedie plate 11 bears a die 1 and, together with the latter, has four punchchannels 12, into which the four punches 3 penetrate when carrying out acut. For this purpose, the die base 13, the die plate 11 and the die 1are moved vertically upwards by means of a piston 61 of a hydraulicdrive with a hydraulic cylinder 6, so that the packaging material 9 isclamped in between the die 1 and the knife part and is cut.

The knives 2 are in each case connected via two knife holders 21 to apiston 22, which is respectively mounted such that it can be displacedvertically in a gas chamber 23 formed in the tool plate 4. On the sideof the piston facing away from the punch holding plate 31, the gaschamber 23 is filled with a gas, for example N₂ or compressed air, whichis under a pressure of up to 300 bar. An annular seal 26 prevents gasfrom escaping from the gas chamber 23 between the chamber wall and thepiston 22. The gas present in the gas chamber 23 forms a compressiblemass which is compressed in the event of a sufficiently high pressure onthe knife 2 and therefore via the knife holder 21 on the piston 22, sothat the piston 22 and the knife 2 can retreat upward. Gas can beremoved from the gas chamber 23 or supplied to it via a gas duct 24, bywhich means the pressure or a limiting force can be set. If a forcelower than the limiting force acts on the knife 2, then the lattermaintains its position relative to the tool plate 4, and if a forcehigher than the limiting force acts, then the knife retreats. Thepressure is preferably set in such a way that a force of typically10–100 N per mm knife length and per mm thickness of the packagingmaterial, but at most 1000 N per mm knife length, acts on the knife 2during cutting.

The stop 25 serves as an indirect support for the knife 2 in theso-called chamfering position. This is because if the packaging material9 is not severed completely, but is only initially cut or chamfered, theknife 2 has to give way even under an extremely small pressure when acut is being carried out, which can be achieved by reducing the gaspressure in the gas chamber 23 by removing gas via the gas duct 24. Whena cut is being carried out, the knife 2 retreats upward until the piston22 rests on the stop 25. By means of vertical displacement of the stop25, here by screwing the latter in or out, the chamfer cutting depth inthe packaging material 9 can be set.

The punches 3 are firmly screwed to the tool plate 4 and are held by thepunch holding plate 31. When a cut is being carried out, they stampstar-shaped holes into the packaging material 9 and penetrate into thepunch channels 12 in the die 1.

In order that the packaging material 9 is separated from the knife partafter a cut has been carried out, the strippers 5 in the tool plate 4are mounted via compression springs 51. The strippers 5 are initiallypressed into the tool plate 4 by the die 1 when a cut is being carriedout, the compression springs 51 being compressed. If the die 1 is thendrawn away downward again, the compression springs 51 expand and ejectthe strippers 5 and the latter eject the packaging material 9 downward.

FIG. 5 shows the chamfer cutting device when cutting packaging material9 in the form of yogurt pots, at the time at which the die 1 and theknife part are at their smallest distance from each other. The left-handknife 2, located in the cutting position, has cut completely through thepackaging material 9 and is touching the die 1, while the right-handknife 2, located in the chamfering position, has only begun to cut orchamfered the packaging material 9.

The cutting position of the left-hand knife 2 results from the fact thatpressurized gas is applied to the gas chamber 23 from a pressurized gasfeed 8, via a pressure reducer 81, a left-hand changeover valve 82 andthe left-hand gas duct 24, and exerts on the left-hand piston 22 a forcewhich is greater than the severing force used for cutting. The necessarysevering force depends on the packaging material 9 to be cut, but isnormally at least 10 N per mm knife length and per mm thickness of thepackaging material. It can be seen that, in the position illustrated inFIG. 5, the left-hand piston 22 has been displaced slightly upward withrespect to the base position illustrated in FIG. 4, that is to say theknife 2 has been displaced upward by the die 1, compressing thepressurized gas present in the gas chamber 23.

By contrast, no pressurized gas has passed into the gas duct 24 and thegas chamber 23 via the right-hand changeover valve 82, so that thepackaging material 9 has forced the right-hand knife 2 upward to such anextent that the right-hand piston 22 has struck the stop 25. The chamfercutting depth in the packaging material 9 results from the verticalposition of the stop 25, which is adjustable by means of screws.

The following definition applies to the whole of the followingdescription. If a figure contains reference signs for the purpose ofclarity of the drawing, but the signs are not explained in theimmediately associated descriptive text, then reference is made to theirmention in the preceding figure descriptions.

SECOND EXEMPLARY EMBODIMENT—FIGS. 6 AND 7

This second exemplary embodiment of a chamfer cutting device accordingto the invention largely corresponds to the first. As distinction fromthe first, however, on the tool plate 104 there are no adjustable stops25 projecting into the gas chambers 123. Instead, the gas ducts 124 arein each case arranged centrally above the gas chambers 123. A chamfercutting device designed in this way is advantageous in particular when aknife 2 sometimes has to be switched away, so that it no longer cuts atall.

THIRD EXEMPLARY EMBODIMENT—FIGS. 8 AND 9

In this third exemplary embodiment, the force-dependent arrangement ofthe knives 2 is not carried out by means of gas pistons but by means oftwo mechanical compression springs 222 in each case, which are arrangedin the tool plate 204. By means of setting screws 223, an opposing orlimiting force produced by the compression springs 222 can be adjusted.In the case of this spring arrangement, after reaching the opposing orlimiting force, the knife 2 begins to retreat, it being necessary forthe force on the knife edge to increase further as the distance by whichthe knife retreats increases. The opposing or limiting force can also beadjusted to the value 0. In this case, the knife 2 begins to retreatupon contact with the packaging material 9. The retreating action takesplace as a function of the cutting force present on the knife 2 and, atthe end of the cutting operation, decreases again until the knife 2contacts the die 1 and the force acting on the knife 2, and thereforethe retreating action, rises again. Otherwise, the construction of thechamfer cutting device corresponds to that of the first two exemplaryembodiments.

FOURTH EXEMPLARY EMBODIMENT—FIGS. 10 TO 12

This fourth exemplary embodiment of a chamfer cutting device accordingto the invention corresponds largely to the third. As distinctiontherefrom, however, the punch holding plate 331 is provided with stops332 for the knife holders 321, which have shoulders 322. In addition, anintermediate plate 333 is in each case arranged between the knifeholders 321 and the compression springs 222.

As can be seen in FIG. 11, during the cutting action, the knives 2arranged in a force-dependent manner are supported on the stops 332 viathe shoulders 322 of the knife holders 321 as soon as the forces actingon the knives 2, through the compression springs 222, reach specificvalues, similar to the way in which this is described in the firstexemplary embodiment for the knives 2 in the so-called chamferingposition. If the forces acting on the knives 2 fall below the forcesdefined by the compression springs 222, for example toward the end ofthe cutting operation, the knives 2 are forced downward against the die1 with the forces defined by the compression springs 222, as shown inFIG. 12.

Instead of being applied by the compression springs 222, the definedforces can also be applied by gas pads or by pads which are formed by aliquid medium, as in the first two exemplary embodiments.

The stops 332 additionally fulfill the function of protecting themechanical compression springs 222 against inadmissibly highdeformations or stresses, by limiting the retreat of the knives 2.

In relation to the chamfer cutting devices described above, furtherconstructional variations can be implemented. Here, mention shouldexpressly be made of the following:

-   -   The knife part can have a large number of knives 2 and punches        3, which can be arranged in an extremely wide range of        configurations.    -   Instead of moving the die 1 toward the knife part when a cut is        being carried out, conversely the knife part can be moved toward        the die 1. Such an arrangement is illustrated in FIG. 13, which        is similar to the first exemplary embodiment illustrated in        FIG. 1. In addition to the elements of FIG. 1, the embodiment of        FIG. 13 includes a hydraulic cylinder 406 and a piston 461 that        is connected to tool plate 404. These elements are respectively        essentially identical to the hydraulic cylinder 6, the piston        61, and the tool plate 4 of FIG. 1 except that, as just        described, the knives 2 move toward the die 1 through action of        the cylinder 406 and the piston 461. As the drive, in addition        to the hydraulic drive shown, thought can also be given to any        other desired drives with which sufficiently high forces can be        produced, such as eccentric or toggle lever drives.

1. A chamfer cutting device for cutting a packaging material, thechamfer cutting device comprising: a die; a tool plate; a knife partincluding at least two knives, at least one of the die and the knifepart being movable relative to the other to cut a packaging materialinterposed between the die and knife part; and a gas piston, wherein atleast one knife of the knife part is mounted on the tool plate via thegas piston so that position of the at least one knife with respect tothe tool plate varies as a function of force produced by contact of theat least one knife with the packaging material or the die.
 2. Thechamfer cutting device as claimed in claim 1, wherein the knife part ismoved toward the die to cut the packaging material.
 3. The chamfercutting device as claimed in claim 1, further comprising means forfeeding gas into and removing gas from a gas chamber of the gas piston,for adjusting dependence of the position of the at least one knife withrespect to the tool plate on the force produced by the contact of the atleast one knife with the packaging material or the die.
 4. The chamfercutting device as claimed in claim 1, wherein the at least one knife ofthe knife part is arranged to retreat so that, when the force producedby the contact of the at least one knife with the packaging material orthe die is less than a limiting force, the at least one knife maintainsposition and when the force produced by the contact of the at least oneknife with the packaging material or the die is greater than thelimiting force, the at least one knife retreats.
 5. The chamfer cuttingdevice as claimed in claim 1, wherein the knife part is stationary andthe die is moved toward the knife part, the knife part havingspring-mounted strippers which, when the packaging material is cut, aretensioned by the die and the packaging material and, when the die ismoved away from the knife part, strip the packaging material from theknives.
 6. The chamfer cutting device as claimed in claim 1, the knifepart further comprising punches which, when the packaging material iscut, punch a hole in the packaging material.
 7. The chamfer cuttingdevice as claimed in claim 1, further comprising means for adjusting amaximum force acting on the at least one knife and produced by thecontact of the at least one knife with the packaging material or thedie, the maximum force not being exceeded in contact between the atleast one knife and the die.
 8. The chamfer cutting device as claimed inclaim 1, wherein the at least one knife comes into contact with the diewhen the packaging material is cut by moving at least one of the knifepart and the die relative to the other.
 9. The chamfer cutting device asclaimed in claim 2, wherein each of the knives in the knife part cominginto contact with the die when the packaging material is cut is mountedon the tool plate via a gas piston, individually or together with otherknives in groups, such that the position of the knives in the knife partwith respect to the tool plate varies as a function of the forceproduced by contact with the packaging material or the die.
 10. Thechamfer cutting device as claimed in claim 1, wherein when the packagingmaterial is cut by moving at least one of the knife part and the dierelative to the other, the force acting on the at least one knife andproduced by the contact between the at least one knife and the packagingmaterial or the die is at most 1000 N per mm of knife length and per mmof thickness of the packaging material.
 11. The chamfer cuffing deviceas claimed in claim 10, wherein when the packaging material is cut bymoving at least one of the knife part and the die relative to the other,the force acting on the at least one knife and produced by the contactbetween the at least one knife and the packaging material or the die is10–100 N per mm knife length and per mm thickness of the packagingmaterial.
 12. The chamfer cutting device as claimed in claim 1,including a stop for each knife of the knife part and on which the knifeis supported during a first part of a cut, in which a first cuttingforce is required, while, during a second part of the cut, in which acutting force less than the first cutting force is required, the knifeis spaced apart from the stop.
 13. The chamfer cuffing device as claimedin claim 12, wherein the stop comprises an adjustable stop.
 14. Thechamfer cutting device as claimed in claim 1, wherein the arrangementsof the individual knives in the knife part can be changed between acutting position in which a knife is located between the tool plate andthe die for cutting completely through the packaging material, and achamfering position in which a knife is located between the tool plateand the die for cutting only partially through the packaging material.15. The chamfer cutting device as claimed in claim 14, including a stopfor each knife of the knife part and on which the knife is supported inthe chamfering position when cutting.
 16. The chamfer cuffing device asclaimed in claim 15, wherein the stop comprises an adjustable stop.